The present invention relates to a display apparatus and a display method for displaying high resolution images by pixel shifting.
Some projection-type display apparatuses, which project an image displayed on a display element onto a screen through a projection lens and the like, change the displayed image based on the installation position of the display apparatus so as to show images which can be correctly seen by observers located in front of the screen even if the installation position thereof is changed. For example, when such a display apparatus is a front projection-type apparatus that normally projects an image from in front of the screen, the display apparatus can also project an image from the back of the screen like a rear projection-type apparatus or can be used upside down like a hanging type apparatus. In the case of rear projection or hanging projection, the display element inverts the image vertically or horizontally according to a control signal so that the image can be correctly projected onto the screen. The image is inverted vertically or horizontally by inverting the order of pixels in which the display element itself writes image information or writing image information which is vertically or horizontally inverted using a storage element such as a frame memory into which the individual pixels of the display element are written.
Generally, using small display elements can downsize the display apparatuses and reduce the cost but this limits the number of display pixels. As a countermeasure for this problem, a so-called pixel shifting technique is proposed. The pixel shifting technique increases the number of effective display pixels by projecting an image while shifting the pixels of the projected image frame by frame. Herein, the frames constitute the image. For example, a display apparatus performing pixel shifting generates image signals C0 and C1 respectively corresponding to odd frames and even frames from an original high-resolution image signal C(x, y) based on the number of pixels of the display element. The display element of the display apparatus alternately displays the image signals C0 and C1 frame by frame. Then, the pixels of the displayed image are shifted and projected using a birefringence device or the like. The display apparatus can therefore display an image composed of an equivalent number of pixels to the original image, which is larger than the number of pixels of the display element.
In such a system, when rear projection is performed using a front projection display apparatus that normally shifts the pixels of C1 to the lower right with respect to the corresponding pixels of C0, the pixels of C1 instead need to be shifted to the lower left with respect to the corresponding pixels of C0. In this case, the display apparatus cannot project a correct image only by horizontally inverting the image using the display element. In a similar manner, in the case of hanging front projection or hanging rear projection, the display apparatus cannot project correct images. These problems can be solved by rotating the birefringence element. However, this requires the display apparatus to include a rotation mechanism which could increase the size and manufacturing cost thereof. Accordingly, a display apparatus is proposed which includes a frame memory between the image signal source and the display element which properly maps an image based on the installation position (see Japanese Patent Laid-open Publication No. 2008-40355).